Short answer
How is an advertising budget decided?
An advertising budget follows what a customer is worth to you, not what a competitor spends. The calculation rests on three numbers: average order value, the margin inside it, and how many clicks it takes to produce one sale. A budget set without those three is a guess; with them, the budget stops being a decision and becomes an output.
Key takeaways
- A budget is not set from a competitor's spend: without knowing their margin, conversion rate and customer lifetime, their number means nothing for you.
- Three numbers are required before any budget: average order value, unit margin and conversion rate.
- Part of the spend in the first months goes to collecting data; treat that as a setup line, not a cost.
- Keeping the daily budget very low does not lower cost — it starves the algorithm of the data it needs to learn and raises unit cost instead.
- If conversion tracking is not in place, the budget conversation is meaningless: every increase made without seeing what works is blind spend.
Which three numbers produce the budget?
The logic is simple: how much of the profit a customer leaves you can you spend to win that customer. If you know your average order value, the margin inside it and how many clicks produce one sale, the maximum you can pay per click falls out on its own. Every click below that figure is profitable, every click above it is a loss.
Find your average order value
Divide six months of revenue by the number of orders. If one-off large orders distort the mean, use the median.
Write down the unit margin
Profit, not revenue. What remains after shipping, commission, returns and packaging — that is the pool advertising can spend from.
Measure the conversion rate
How many visits produce one sale. If that number does not exist, month one's job is not raising budget but setting up conversion tracking.
Derive the maximum cost per click
Divide unit margin by the number of clicks a sale takes. The result is your ceiling per click; your bids belong under it.
When should you raise the budget?
The decision to increase is made on unit cost, not at month end. If acquisition cost sits below your ceiling and demand is still unmet, raising the budget produces profit directly. If acquisition cost is approaching the ceiling, the problem is not budget: either the conversion rate or the targeting is too narrow. Confusing those two is the most expensive mistake in advertising.
Frequently asked
Can you start with a small budget?
- You can, but a very small daily budget does the opposite of what is expected: the campaign never gathers enough data to learn which searches work, and unit cost stays high. The more efficient route is to concentrate the budget on one product and one region rather than spreading it across the whole country and catalogue.
How much of the budget should go to brand versus sales?
- Until the measurable sales channels are saturated, it is more sensible not to split. Allocating budget to a brand campaign while there is still unmet demand on buying-intent searches moves measurable profit into an unmeasurable line. Once the sales channel saturates — that is, once raising budget starts raising unit cost — moving to the brand side makes sense.
Sources
- 01How the Google Ads auction works — Google Ads Help, 2026
- 02Quality Score — what it is and what it is not — Google Ads Help, 2026
Queries this page answers
- how to set an ad budget
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